1. Field of the Invention
The subject matter disclosed generally relates to the field of semiconductor lasers.
2. Background Information
Conventional laser diodes, which are fabricated from III-V compound semiconductors such as GaAlAs, InGaAlP and InGaAsP operate at wavelengths between 0.4 and 1.6 μm. Longer wavelengths in the mid-infrared range between 2 and 10 μm are required for important applications, including:                Optical communications in the open atmosphere, which are highly vulnerable to scattering by fog and rain at conventional diode wavelengths shorter than 2 μm. By contrast, the atmosphere is much more transparent to wavelengths around 10 μm, where attenuation through fog can be as much as 150 db/km lower.        Measures to protect civilian and military aircraft from attack by shoulder-fired missiles, which use transmission of optical pulses in the 2 to 4.5 μm band to confuse their heat-seeking guidance systems.        The presence of chemical weapons such as nerve agents, as well as environmental pollutants can be sensitively detected by monitoring atmospheric absorption of mid-infrared laser beams.        
There are unfortunately no practical laser diodes in this wavelength region. Diodes using Quantum Cascade designs have been demonstrated, but these have very low efficiency and require cryogenic cooling that makes them impractical for most applications.
It would be desirable to provide a semiconductor laser that efficiently generates light in the mid-range of infrared without some or all of the drawbacks found in prior art devices.